The present invention relates generally to a ski boot and more particularly to a ski boot intended for use in cross-country skiing, sometimes variously referred to as long-distance skiing or langlauf skiing or Nordic skiing; for the sake of convenience, the term cross-country skiing will be used in this specification. The invention is even more particularly concerned with a manner of securing a cross-country ski boot to an associated ski, and thus also concerns a base plate adapted to be secured to a ski and to co-operate with a ski boot.
In one form of cross-country ski boot, the sole thereof is provided with a front extension portion by means of which the sole can be secured to the top surface of the ski by means of a suitable ski binding. A rib and groove respectively extend in the longitudinal direction of the ski and the sole of the boot and when they come into positive co-operation with each other, they provide an additional support in a sideways direction for the foot of the skier, in addition to the holding action of the ski binding. It should be noted that, in cross-country skiing, the heel of the boot is lifted from the surface of the ski as the skier moves, with a rolling action somewhat similar to a normal walking action, thus contrasting with a downhill skiing motion in which the boot is firmly fixed to the ski both at the front and at the rear. Thus, when cross-country skiing, when the sole of the boot is moved back towards the top surface of the ski from the position of the boot in which the heel is raised therefrom, with the sole of the boot thus being somewhat curved, the longitudinal rib and groove come into increasing engagement with each other and thus prevent the boot from being deflected sideways, by virtue of the positive co-operation between rib and groove. In order to ensure that the sideways support for the boot on the ski comes into effect as early as possible in the movement of the boot on the ski, the longitudinal rib and groove may be so arranged as to extend as far as the tip of the sole or the front extension portion thereof. Nonetheless, when the boot is in a position in which the heel and a substantial part of the sole of the boot are lifted away from the top of the ski, it will be seen that there is at best a minimum condition of engagement between the longitudinal rib and the longitudinal groove so that, in that position of the boot and also in the first phase of the downward movement of the boot towards the ski, the sideways support action afforded by the interengagement of the rib and the groove is correspondingly slight. That is particularly noticeable in the case of those combinations of ski boot and ski binding in which the cross-country ski boot is held in position by the ski binding at a very far forward position, that is to say for example either at the front edge of the sole, as disclosed for example in DE-AS (German published specification) No. 26 22 966, or by means of a comparatively narrow front extension portion on the sole, for example as disclosed in DE-AS No. 26 10 041, with the front extension portion acting as a rolling tongue portion to permit the boot to roll and lift in relation to the surface of the ski, as referred to above. It will be appreciated that, with such arrangements, the holding forces produced by the ski binding are applied to the sole of the boot over a locally restricted portion thereof so that it is not possible for lateral bending and torsional deformation of the sole of the boot to be prevented satisfactorily under all circumstances. Although the interengageable longitudinal rib and groove may be of such a configuration that they can still come into engagement with each other, even when they are laterally displaced relative to each other to a certain degree, and have to a certain extent an alignment function, for example by virtue of the side surfaces of the rib and groove being inclined to give a form of centering action, nonetheless when the rib and the groove are somewhat more severely displaced relative to each other in a sideways direction, the above-mentioned alignment function or centering action is unpleasant from the point of view of the skier insofar as a shock or impact can be felt when the sole of the boot is set down on to the top surface of the ski and the rib and the groove adjust relative to each other so as to come into mutual engagement. In the limit case, when the rib and the groove are displaced laterally relative to each other to a particularly large degree, they may no longer come into engagement with each other, with obvious detrimental results.